1. Field of the Invention
The present invention relates to enzymes that hydrolyze lysophospholipids in tissues.
The present invention particularly concerns a new, cloned human brain lysophospholipase, its kinetic parameters and of its potential role in treatment of disease states having elevated concentrations of lysophospholipids, including atherosclerosis, hyperlipidemia, lethal dysrhythmias in myocardial ischemia and segmental demyelination of peripheral nerves.
2. Description of Related Art
Lysophospholipases (LysoPLA) are important enzymes that hydrolyze lysophospholipids (LysoPL). LysoPLs are detergent-like intermediates in phospholipid metabolism and play essential roles in many physiological and pathological processes. Lysophosphatidylcholine (LysoPC), a normal constituent of cell membranes, may act as a lipid messenger, transducing signals initiated from membrane receptors. Exogenous addition of LysoPC to cultured cells regulates the expression and/or activity of a variety of proteins including nitric oxide synthase, IL-1β, transcription factor nuclear factor-kappa B, activator protein 1, c-Jun N-terminal kinase, heparin-binding epidermal growth factor-like growth factor, cellular adhesion molecule-1 and many other proteins. LysoPC also modulates intracellular Ca 2/levels, stimulates the release of arachidonic acid in human endothelial cells and rat mesangial cells through a pathway that involves the activation of PKC and cPLA2. Lysophosphatidic acid (LPA), the simplest natural occurring LysoPL, is a multifunctional phospholipid messenger that evokes a variety of biological responses, ranging from platelet aggregation to smooth muscle contraction, from cell proliferation and differentiation to focal adhesion assembly and stress fiber formation. Such diversified biological responses to LPA appear to involve the activation of a specific G-protein coupled receptor, which in turn couples to multiple independent effector pathways including the small GTP-binding proteins Ras and Rho. Indeed, LPA-specific receptors were cloned recently and identified as members of the G-protein coupled receptors. Increased LysoPL levels have been detected in a variety of disease states including atherosclerosis, hyperlipidemia, lethal dysrhythmias in myocardial ischemia and segmental demyelination of peripheral nerves. Accumulation of LysoPL can perturb the activities of many membrane-bound signal-transducing enzymes, distort cell membrane integrity and even lead to cell lysis.
These increased LysoPL levels are believed to result from the dysfunction of LysoPL-regulating enzymes. Since LysoPLs play such diversified roles, their levels must be strictly regulated for proper cell function and survival. LysoPLA, which controls LysoPL levels through hydrolysis, has been identified in a variety of cells and tissues. Recently, a rat and a mouse LysoPLA have been sequenced, cloned and expressed. These two enzymes (both of 25 kDa molecular mass) share high sequence homology and exhibit similar properties. They are new members of the K/L hydrolase family with a catalytic site composed of Ser-119, Asp-174 and His-208.